User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20170817100132 Steps to reproduce: My current setup is: - Ubuntu Xenial 16.04.3 LTS x86_64 - Linux kernel 4.10.0-32-generic - Firefox 55.0.1+build2-0ubuntu0.16.04.2 - Firefox Nightly (latest build) Steps to reproduce: 1) Go to this web page: https://mcforge.readthedocs.io/en/latest/gettingstarted/structuring/ 2) In that web page find a chunk of code sample made with <code> tag and that has a visible horizontal scrollbar. For this example you can use the JSON code from the "The mcmod.info file" section. 3) Hover the mouse over the sample code 4) Sroll with your mouse wheel Note: I have tested this on Windows 10 x86_64 with Firefox Nightly and there is no stutter. Actual results: Firefox stutters when scrolling. If you scroll further so that you can't see the code sample the stutter will disappear, but if you scroll again to the code sample area the stutter returns. The stutter disappear after several seconds or when you reload the web page. Expected results: No stutter.